This program first seeks an understanding of the reasons for the increased complexity of epididymal function and development of the need for capacitation of sperm in the female tract during evolution of eutherian mammals. This will be approached in a wide variety of non- mammalian vertebrates, in a monotreme, in marsupials, and in testicondid (non-scrotal) eutherian mammals. As well as the androgen dependence of the storage of sperm in the male and, in selected cases, their fertilizing ability, the specific parameters of sperm to be studied include the capacity for motility, the character of the surface of the plasmalemma, the structural quality of the nuclear chromatin and tail fibers, and the ultrastructure of the sperm head. The claim that there are changes during epididymal maturation in the competence of the sperm genome to support normal development will be studied by transfer of fertilized eggs and evaluation of their development, and the question of aging deterioration of sperm DNA in the female tract will be investigated by use of a system which prolongs the fertile life of sperm in the female. The effects of vasectomy on sperm disposal by the androgen-deficient and normal epididymis, and its effect on spermatogenesis will be studied by electron microscopy and autoradiography. Using surface labelling techniques, phytoagglutinins and anti-egg antibody, together with experimental manipulation, aspects of fertilization to be investigated include: maturation of the vitelline surface of the follicular oocyte in rabbits and rodents; the stimulus for the acrosome reaction; the mechanism of sperm penetration of the zona pellucida; factors involved in decondensation of the sperm head in the ooplasm.